1. Field of the Invention
The present invention is directed to a gearless speed and torque converter. More specifically, the present invention is directed to an in-line speed and torque converter wherein balls undergo motions in Archimedes spiral grooves to convert speed and torque in several stages.
2. Brief Description of the Prior Art
Speed reducers, torque converters, gear boxes and the like have been known for a long time. A serious disadvantage of most prior art torque converters or gear boxes is that a relatively large amount of energy is lost to friction during torque conversion. The energy loss is particularly serious in gear boxes or gear trains employing a worm gear-pinion gear combination, where at relatively low speeds often more than half of the inputted rotational energy is lost to friction.
Another disadvantage of conventional gear boxes is that they are usually relatively bulky, and often hard to adapt to function as in-line torque and speed converters.
In order to overcome the well known disadvantages of conventional "gear boxes," the prior art has also provided speed and torque converters which utilize an eccentric or "nutation" type drive in combination with conventional gears. Such a device is shown, e.g., in U.S. Pat. No. 3,895,540. Eccentric drives have also been combined in the prior art with balls moving in scalloped tracks to provide torque conversion without the use of conventional toothed gears. Such a device is disclosed in a brochure titled "Anti-Friction Drive" by Advanced Energy Technology, Inc. of Boulder, Colo.
U.S. Pat. Nos. 2,749,761 and 2,764,030 are of particular interest to the present invention because these two patents disclose gearless speed and torque converters, which utilize a plurality of balls moving in spiral grooves machined into adjoining surfaces to provide speed and torque conversion.
More specifically, U.S. Pat. No. 2,749,761 purports to disclose a speed reducer which has two members mounted adjacent to one another on parallel but not colinearly disposed axes. The driving member has spiral grooves incorporated into its outer surface and the driven member has spaced radial ribs incorporated into its outer surface. A closed loop ball conduit having a plurality of balls is located adjacent to the driving and driven members and has an opening at a location where the spiral grooves and the radial ribs interface with one another. The balls continuously circulating in the loop are said in the patent to transmit power with a minimum amount of rubbing friction.
U.S. Pat. No. 2,764,030 purports to disclose a coaxial speed-reducing device wherein the driving member and the driven member both have spiral grooves machined into their adjoining surfaces. A plurality of balls are held between the adjoining spiral groove-bearing surfaces by the grooves and by a fixedly mounted ball race or ball retainer which has radial slots to allow movement of the balls only in a radial, outward direction. Speed reduction of the device is determined by the pitch ratios of the spiral grooves of the driving and driven members. The speed-reducing device is said in the patent to be durable, to require only a minimum amount of lubrication and to be suitable for use in a wide range of speed-reduction ratios.
The speed-reducing devices disclosed in the above-noted U.S. Pat. Nos. 2,749,761 and 2,764,030, however, suffer from extremely serious disadvantages regarding the amount of lubrication needed to keep the device even marginally operational, regarding the speed reduction achievable by the devices, and, most importantly, regarding the energy efficiency and the ability of the devices to transmit torques of significant magnitude. This is because the ball race or ball retainer (designated, e.g., 19 in FIG. 5 of U.S. Pat. No. 2,764,030) prevents the balls from undergoing an orbiting or circulating motion about the common axis of rotation of the driving and driven members, and allows only for their radially outward-bound motion. In the device disclosed in U.S. Pat. No. 2,749,761 the ball conduit (designated 22, e.g., in FIG. 1 of the patent) plays a similar role restricting movement of the balls.
As it becomes more apparent from the ensuing description of the present invention, in a device wherein torque is transmitted by a plurality of balls from one rotating member to another, the balls must be allowed to move freely in a circulating or orbiting motion (simultaneously with a radial motion) in order to operate with low friction. In the absence of this freedom of motion, as in the devices disclosed in U.S. Pat. Nos. 2,749,761 and 2,764,030, the balls necessarily slide between the two rotating surfaces. As is well understood by those skilled in the mechanical arts, significant sliding motion is simply incompatible with operation even at moderate efficiency and for transmission for anything other than minimal amounts of torque. Furthermore, a device wherein undesirable sliding motion occurs during power transmission necessarily has an unacceptably short operating life.
In light of the foregoing and other reasons, a significant need still exists in the prior art for efficient torque conversion devices, and especially for efficient in-line speed-reducing torque conversion devices. The present invention satisfies this need.
To provide further background to the present invention, and generally to the state-of-the-art relating to ball screws and the like, reference is made to U.S. Pat. Nos. 2,874,594; 2,711,655; 3,046,808; 3,302,477; and 4,221,137.